Scanning antenna



April 29, 1947- c. B. H. FELDMAN' 2,419,556

S CANN ING ANTENNAS Filed July 22, 1942 2 Sheets-Sheet 1 INVE N TORC.B.H.FELDMAN A TTOQNEY 3 April 29; 1947. v 'c. B. H. F LDMAN 2,419,556

SCANNING ANTENNAS Filed July 22, 1942 2 Sheets-Shet? RELZTIVE FIELDANGLE/N Mans/=25 5O '45 4O 35 3O 25 '20- 15 "IO '5 O 5 IO 15 20 2,5

DIRECTIVE CIMRACTER/ST/C-ELECTRIC PLANE RELATIVE new I so 13 1'0 3'5 '30'2': 1'0 [5 -|o o v 5 I0 I: 20*

- I DIRECTIVE 'CHARACTERI$TICMAGNET/C PLANE INVENTOR B. H. F E LDMAN BYv MM ATTORNEY Patented Apr. 29, 1947 UNITED STAT-ES PATENT OFFICESCANNING ANTENNA can B. H; Feldman, Rumson, N. J., assignoritoBell'lelephone Laboratories, Incorporated, New

York, N. Y., a corporation of- New- York Application July 22, 1942,Serial No. 451,932

9 Claims.

This. invention relates to. directive antennas, and more. particularlyto directive antennas. of the type used in direction finding and radioscanning systems. I

As is known, the peak of the maximum lobe, considered in the solid, ofeven the most highly unidirectional antenna unit at present in use forsignal or intelligence communication, is relatively blunt or flat overan angular range includ-.

ingalarge number of distinct paths or linear wave directions. The lobeis therefore ordinarily not sufiiciently pointed or sharp to secure thehigh degree ofdirective selectivity required for direction determinationin airport landing, radar and scanning systems; In order to secure amore accurate wave direction determination, than is obtainable'with theprior art antennas of the signaltype, at least three distinct types ofantenna arrangements have been suggested for use in the shortwave andultra-short scanning or objectlocating field. Thus, Patent 2,002,181 toW. Ilberg illustrates a lobe switching arrangement; Fig. 3 of Patent2,083,242 to W. Runge illustrates a "lobe sweeping m-ultiunit array, andFig. 2 of the aforementioned Runge patent illustrates alobe rotationantenna system. The present invention relates primarily to antennas ofthe lobe rotation type and, while-scanning antennas of this type. havebeen used in the past with some successin the short and ultra-short wavefields, it now. appears desirable to utilize this type of scanningantenna in the microwave field and to obtain an improved lobe rotationantenna systemhaving certain distinct mechanical and electrical featuresnot found in the prior art arrangements.

It is one object. of this invention to increase the directivesensitivity of an antenna.

It is another object of this invention to determine accuratelythepropagation direction of a transmitted or received radio wave.

It is still'another object of this invention to utilize, in a loberotation antenna system, simple lightweight apparatus for producing thelobe rotation.

It is afurther object of this invention to adjust or vary, in a loberotation system, the angle between the maximum lobe of the antenna andtheantenna axis.

It is an additional: object of this invention to provide, in a loberotation antenna system, means for adjusting the shape of the maximumlobe and the intensity relation of the-maximum and minor lobes-Inaccordance with thepreferred embodiment of the invention, the antennasystem comprises a large paraboloidal reflectonia dipole at the focusthereof, and a small semispherical reflector facing theparaboloidalreflector andhaving itsopening spaced slightly from thefocal plane of the paraboloidal reflector. A translation device, such asa radio range transceiver, is connected to the dipole. Means areprovided for rotating the spherical reflector in a manner such that itsprincipal axis revolves about the principal'axis of the paraboloidalreflector and its electro-optical'focus describes, in effect, a circle.Rotation of the spherical reflector produces conical rotation of themaximum directive lobe of the antenna, the angle between the axis of theparaboloida1 reflector and the principal axis of the maximum lobe beingmaintained at a constant value during the lobe rotation, so that theprincipal lobe axis describes in. space a cone having its apex at thecenter point of" the, antenna, substantially, If desired, the spacingbetween the axes of the two, reflectors, may be adjusted for the purposeof changing, the conical searching range. If the spacing is relativelysmall, the conical angle is small and-the lobe rotates about the axis ofthe paraboloidal reflector so that, assuming the minor lobe axis isaligned with a target, the reflected signals are ofthe same intensity.If the spacing is. large the conical angle is large. In addition, thespacing between the reflectoropenings may be adjusted for the purposeofsecuring an optimum gainer anoptimum directive characteristic.

The invention will. be more fully understood from a perusal of thefollowing specification taken in conjunction withthe. drawing on whichlike reference characters denote elements of similar function, andonwhich:

Figs. 1 and2 are, respectively, a cross-sectional view, taken inelevation, and a front view of the.

preferred embodiment of the invention;

Figs. 3. and 4 are curves illustrating the measured' directive-patternsof the preferredembodiment; and- Fig. 5 is a diagram used in explainingone featransmitter orreceiver, or it may be a transceiver of the typeemployed in conventional radio range systemsof the pulse type. Numeralsdesignates such that the openings 4 and i3 are always par allel, theaxes 3 and 12 are always parallel, and

the center H describes a circle about the focus 2, substantially. Themeans for rotating reflector 10 comprises a motor I l, belt l5, drivingshaft [6 supported on bearings II, the stationary tubular elbow memberl8, and the movable L-shaped rod I9 which is connected to the rear ofreflector ID at a point 20 spaced from the axis l2. The L-shaped rod l8extends through the vertical portion of the elbow member l8 and isadjustably connected thereto by means of a set-screw 2|, so that thespacing between the axes 3 and 12, corresponding to the radius ofrotation of reflector It, may be altered. Also, the shaft l6 extendsthrough the horizontal portion of elbow I8 and is adjustably connectedthereto by means of setscrew 22, whereby the spacing between thereflector openings 4 and I3 may be changed.

In operation, assuming the antenna system is used for transmittingpulses in a microwave radio scanning or radar system, pulses aresupplied by device 8 over line 1 to dipole 6. At the same time thespherical reflector is rotated by motor I4 in a clockwise directionabout the axis 3 of the paraboloidal reflector, as indicated by thecircular arrow 23, Fig. 2. In the plane perpendicular to the dipole,hereinafter called the magnetic plane, the energy is radiatednon-directionally by dipole 6. In the plane of the dipole, hereinaftercalled the electric plane and corresponds to the plane of the drawing(Fig. 1), the radiatiton is not completely non-directional but may beconsidered to be so, since the dipole is positioned in the focal plane 5of reflector l and is relatively small compared to the reflectors.Considering any plane passing through the focus 2, certain of thewavelets emitted by the dipole pass directly to the paraboloidalreflector and, in a manner well understood in the art, these particularwavelets are reflected so that their propagation directions extend insubstantially parallel lines. Certain other wavelets emitted by thedipole 6 impinge upon the semispherical reflector, are reflected therebyso as to strike the paraboloidal reflector and are then projected intothe ether medium through the opening 4 of paraboloidal reflector I.Since many of these last-mentioned wavelets do not pass through thefocus of the paraboloidal reflector, the wavelets reflected by both thespherical and the paraboloidal reflectors combine with the waveletsreflected only by the paraboloidal reflector to produce a maximum lobeor beam having its principal axis at an angle to the axes 3 and E2 ofthe reflectors. Thus, for example, with the spherical reflector 10 inthe top position, as shown by the full-line illustration of thisreflector in Fig. 1, the principal axis of the maximum lobe is pointeddownwards as illustrated byarrow 24. With the reflector In in the bottomposition, as illustrated by the dotted line representation in, theprincipal axis is directed upwards as shown by arrow 24. Hence therotating spherical reflector causes thev longitudinal axis and the peakof the maximum lobe to rotate about the axis 3, the base of the lobebeing fixed roughly at the mid-point 25 of the paraboloidal reflector.In other words, the reflector rotation causes the principal axis of thelobe to describe in space a cone-shaped figure.

Referring to Figs. 3 and 4 of the drawing, Fig. 3 illustrate the shapeand the two positions, as measured in the electric plane, of thedirective pattern; and Fig. 4 illustrates the shape and the twopositions of the pattern, as measured in the magnetic plane, for asystem constructed in accordance with the invention. Numerals 26 and26', Fig. 3, denote the two positions of the maximum electric plane lobeand numerals 21 and 21', Fig. 4, designate the two positions of themaximum magnetic plane lobe. Thus, the full-line and dotted-line curves26 and 26' correspond, respectively, to the top and bottom positions ofthe rotating reflector ID; and curves 2! and 21' correspond to the rightand left positions of reflector H]. In the system actually tested, analuminum paraboloidal reflector having a focal length of 8.66 inches anda diameter of thirty inches, and a copper semispherical reflector havinga six inch diameter were used, the spacing between the axis 3 and thepoint 28 of connection between rod l9 and reflector l0, being about oneinch. In other words, in accordance with the invention, the ratio of theparaboloidal reflector diameter to the semispherical reflector diameteris in the order of flve whereby, as shown on the drawing, the minorelectric plane lobes 28 and 28 and the minor magnetic plane lobes 29 and29' are rendered negligible.

Referring to Fig. 5, the conical angle 30 between the principal axis 3!of the maximum lobe 2 and the axis 3 may be altered, if desired, bysliding the vertical rod or arm 19 within the elbow member !8 andsecuring these elements together by the set-screw 2|. In other words,referring to Figs. 3 and 4, the spacing 34 between the two positions fortheprincipal axis 3| of the maximum lobe, may be changed by adjustmentof rod I9. For accurate direction determination, the spacing between thecenter H and axis 3, Fig. l, is preferably made relatively small,whereby a small conical angle 35, Fig. 5, is obtained. The maximum lobe32 or its principal axis 3| is, in eifect, rotated about a subordinateradius 36 of the maximum lobe and, assuming the radius or line 36 isaligned with a target, the received reflected pulses have a constantintensity. If desired, the entire antenna assembly including the tworeflectors may be moved Vertically and/or horizontally as inconventional radar or scanning systems. Also, referring to Fig. 1, ifdesired, the shape of the nose of the maximum lobe may be altered, thatis, sharpened or flattened, and the optimumratio of the intensities ofthe maximum to minor lobes may be obtained, by adjusting shaft l6relative to the fixed elbow member 18 and thereby adjusting thehorizontal spacing between dipole 6 and the reflector l0.

Although the invention has been explained in connection with a certainembodiment, it should be understood that it is not to be limited to theembodiment described inasmuch as other apparatus may be utilized insuccessfully practicing the invention. Thus, in place of the dipole andassociated coaxial line an open wave guide having its aperture at thefocus 2 may be employed for emitting or, collecting the waveletsimpinging on the reflectors and H1. Also, if desired, a cylindricalparabolic or other concave reflector may be used in place of theparaboloidal re-' flector.

What is claimed is:

1. In combination, a translation device, an antenna system comprising aspherical reflector having a principal axis, an antenna member connectedto said device and spaced from the reflector axis in the plane of thereflector opening, and means for moving the reflector axis relative tosaid member, whereby steering of the maximum directive lobe is effected.

2. In combination, a translation device, an antenna system comprising aspherical reflector having a principal axis, an antenna member connectedto said device and spaced from said reflector axis in the plane of thereflector opening, and means for rotating the reflector axis about saidmember, whereby the directive lobe of said antenna system is rotated.

3. In combination, a paraboloidal reflector, an antenna positioned atthe focus thereof, a semispherical reflector facing said paraboloidalreflector, and means for rotating the axis of said semisphericalreflector about the axis of the paraboloidal reflector.

4. In combination, a parabolic reflector, a dipole at the focus thereof,a spherical reflector facing said parabolic reflector and means forrotating said spherical reflector so as to cause its electro-opticalfocus to describe a circle about the axis of the parabolic reflector.

5. In combination, a parabolic reflector, a transceiver, an antennaconnected to said transceiver and positioned at the focus of saidreflector, a semispherical reflector, said reflectors facing each other,the axes of said reflectors be ing parallel and spaced from each other,whereby maximum radio action occurs at an angle to said axes.

6. In combination, an antenna system comprising a first concavereflector having a focus and a principal axis, an antenna element foremitting and absorbing energy positioned at said focus, means forcausing rotation of the directive lobe of said system comprising asecond concave reflector completely facing the first-mentioned concavereflector and having a principal axis positioned parallel to the firstmentioned principal axis, and means for rotating the axis of the secondreflector about said first mentioned principal axis.

'7. A radio scanning system comprising a pair of concave metallicreflectors having their openings facing each other and each having aprincipal axis, an antenna included between said reflectors, and meansfor rotating the axis of one reflector about the axis of the otherreflector and maintaining said axes parallel.

8. In combination, a paraboloidal reflector, an antenna element locatedat the focus thereof, a semispherical reflector, the principal axes ofsaid reflectors being parallel and spaced a given amount, and means forchanging the spacing between said axes.

9. In combination, a paraboloidal reflector, an antenna element at thefocus thereof, a semispherical reflector, said reflectors facing eachother, and means for changing the spacings between the openings of saidreflectors.

CARL B. H. FELCDLlAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,173,897 Clavier Sept. 26, 19392,083,242 Runge June 8, 1937 2,043,347 Clavier et al June 9, 1936FOREIGN PATENTS Number Country Date 370,135 British Apr. '7, 1932

